"With regard to Iran, some of the reports that we've seen about an agreement on nuclear matters or, for that matter, on detainees, are simply not accurate and not true," Blinken said when asked about indirect talks via Oman.

On Monday Iran said it was conducting indirect negotiations with the United States through the Sultanate of Oman, with nuclear issues, US sanctions and detainees on the menu.

That sparked reports that the two sides, who haven't negotiated directly for years, could be closing in a deal.

"We welcome the efforts of Omani officials and we exchanged messages with the other party through this mediator" over the lifting of US sanctions, Iran's foreign ministry spokesman Nasser Kanani said Monday.

"We have never stopped the diplomatic processes," he added, emphasizing that the talks "were not secret."

The two sides have been unable for two years to reach a deal on President Joe Biden's desire to revive the 2015 deal which granted Tehran much-needed sanctions relief in exchange for curbs on its nuclear program.

Biden's predecessor Donald Trump unilaterally withdrew from the deal in 2018, and since then Tehran has steadily progressed in development of its nuclear industry, though not -- as feared -- producing a nuclear weapon.

Iran's supreme leader Ayatollah Ali Khamenei reiterated last week that the country does not intend to acquire a nuclear weapon.

Khameini said deals could be reached with the United States, provided they do not change "the existing infrastructure of the nuclear industry."

Kanani on Monday said a prisoner exchange could be agreed "in the near future," provided that Washington exhibits "the same level of seriousness" as Tehran.

At least three Iranian-Americans are being held in Iran, including businessman Siamak Namazi, arrested in October 2015 and sentenced to 10 years in prison for espionage.